Manifestation of carrier relaxation through the manifold of localized states in PCDTBT:PC60BM bulk heterojunction material: the role of PC84BM traps on the carrier transport.

The transport and relaxation of photogenerated carriers in a bulk heterojunction (BHJ) material made of a blend of PCDTBT and PC(60) BM are studied as a function of the concentration of PC(84)BM impurities. For low concentrations of PC(84)BM, the increasing activation energy with delay time indicates transport dominated by trap-limited carrier drift while the photocarriers relax through a manifold of disorder-induced localized states near the band edge. In the BHJ material with high concentration of PC(84)BM, transport is dominated by carrier hopping within the PC(84)BM impurity band.